Robots are extensively used in the industry for applications such as electronic circuit board assembly and other automated assembly tasks. The particularly high popularity of modern robots is attributed to their simple construction, low cost, low maintenance, light weight, high accuracy, high speed and compliance characteristics.
Generally, the programming of robots used in industry requires specialized knowledge and can only be performed by persons skilled in the art, often referred to as system integrators. In connection with multi-purpose robots for use in industry or even at home some important safety issues still remain unsolved.
A conventional robot system is provided with a collision detection function which detects collision of a robot with its surroundings based on abnormal torque generated at the manipulator part of the robot. If collision is detected by this collision detection function, control is performed to stop the operation of the robot or otherwise lighten the collision force. Due to this, the damage to the robot and the devices provided at the robot as well as surrounding equipment is kept to a minimum.
However, when using a collision detection function for detecting collision between a human and a robot, it is necessary to raise the sensitivity to collision in order to ensure safety of the human. For this reason, it is sought to precisely estimate the frictional torque of the gears or speed reducers etc. provided at the different parts of a robot. In this regard, the frictional torque fluctuates depending on the outside air temperature and the operating state of the robot, so estimating the frictional torque with a high precision is difficult. Therefore, it was difficult to precisely detect collision between a human and a robot from the torques of the manipulator part of a robot and prevent harm to the human.
However, when a human directly contacts a robot without a carried object interposed between them, the force which occurs between the human and the robot is not detected. Further, even if attaching a force sensor for detecting force between the arm and hand of a robot etc., it is not possible to detect contact of the human at the arm portion of the robot which the sensor cannot detect. For this reason, in the prior art, it was not possible to provide a robot system which enabled safe interactive work when there was a possibility of a human and a robot coming into direct contact.
Capacitive sensors have been used to measure capacitance changes, which are caused in the electric field of the capacitor formed by the sensor as a result of the approach of an object. In addition to all electrically good conducting materials, capacitive sensors only detect those materials having an adequately high permittivity. Capacitive sensors are not useful as a safety device in the case of rapidly moving apparatuses with solid parts moved freely in space. In this connection a complete system is desirable, which permits a reliable human-machine cooperation.
A robot is a physical machine which can potentially be dangerous and cause harm to humans by colliding with them. In case of hardware or software defects, the robot might even do unexpected motions, which were not anticipated by the system integrator (the person responsible for the safety when setting up the robot). For this reason, it can be very desirable for a robot to have an improved safety system.
US2010/0324733 discloses a robot with a safety system comprising a joint, a first torque sensor and a second torque sensor mounted at each joint. Torque sensors (such as straing gagues) are not applicable for obtaining a reliable safety control system. Moreover, the sensors in US2010/0324733 are connected to two computing units S1, S2 in the form of integrated circuits (ICs), which have microcontrollers, within a transmitter unit S. Thus, US2010/0324733 does not have all sensor circuits placed on the same component, which renders it less applicable for safety control.
The problem of the invention is to provide a safety device for the operation of apparatuses with parts freely movable in space, which permits the reliable and safe operation of such apparatuses without complicated and costly peripherals and which also ensures that collisions between apparatus parts and humans or objects are detected reliably at an early stage, so that in addition to avoiding planning and production costs there is a considerably reduced space requirement for such installations, so that in future people and machines can jointly use working areas.